Turbulence readily arises in numerous flows in nature andtechnology. The large number of degrees of freedom ofturbulence poses serious challenges to numerical approachesaimed at understanding and controlling such flows. While theNavier-Stokes equations are commonly accepted to preciselydescribe fluid flow, including turbulence, alternative coarseneddescriptions need to be developed. These coarseneddescriptions aim at capturing the primary features of a flow, atconsiderably reduced computational effort. Such coarseningintroduces a `closure problem' that requires additionalphenomenological modeling. Careful analysis andfundamental understanding of turbulence and numericalmethods are needed to achieve successful closure and accuratecomputational strategies.

An overview of the large-eddy simulation (LES) approach issketched in which we present the phenomenology of coarsenedturbulence, linking RANS and LES and discussing the centralclosure problem. Sub-filter modeling is reviewed and severalmodels

proposed in literature are discussed, includingeddy-viscosity models, dynamic models, regularizationmodels, variational multiscale approach and approximateinverse modeling. Testing of LES computational strategies isdiscussed and illustrated for (i) homogeneous, isotropic,decaying turbulence, (ii) turbulent mixing and (iii) separatedboundary layer flow. Error-assessment for large-eddysimulation is given attention; predictions of LES areprincipally flawed due to shortcomings in the closure modelingand errors in the numerical treatment. A systematic frameworkfor estimating these errors is presented, error-decomposition isillustrate and the error-landscape concept is introduced andadopted for optimization of numerical and model parameters.Finally,an illustration of the error-landscape approach toturbulent combustion is provided.